Download Gene Regulation III Reminder

Gene Regulation III
Reminder
• Exam Friday
Review
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DNA ➞ RNA ➞ protein
Every cell in body has same DNA.
Not all cells make all proteins
What turns genes on and off?
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Prokaryotes
•small (1000x)
•no nucleus
•no membranebound organelles
•1 main
chromosome
•some plasmid
•about 4000 genes
•genes in operons
Promoter Operator
gene A
gene B
gene C
Lac Operon - Negative Control
lac i
Promoter Operator
Lac z
Lac y
Lac a
repressor
!4
Lac Operon - Inducible
lac i
RNA
PolymerPromoter Operator
ase
Lac z
BG-
Lac y
Lac a
P
TA
Lac Operon - Positive Control
lac i
RNA
CAP
PolymerPromoter
Operator
ase
cAMP
Lac z
BG-
Lac y
Lac a
P
TA
!6
Trp Operon
trp r
inactive
repressor
RNA
Polymer- P
ase
O
trpE trpD trpC trpB trpA
E-
D
C
B
A
Trp Operon - Repressible
trp r
RNA
PolymerP
ase
tryptophan
O
trpE trpD trpC trpB trpA
Transcription/Translation
Simultaneous
DNA
trp E
• Prokaryotes no nucleus
trp D
trp C
trp B
trp A
Transcription
mRNA
Translation
Attenuation/Leader
mRNA
4
Low trp in env.
•Translation of 1 slow
•2-3 loop forms
•transcription of
complete mRNA
1
4
3
1
trpE trpD trpC trpB trpA
3
2
L
2
High trp in env.
•Translation of 1 fast
•3-4 termination hairpin forms
•inhibits further transcription
Eukaryotes
• have nucleus
• have membranebound organelles
• cells larger
• DNA in nucleus
• DNA linear
• Transcription &
translation separate
places (nucleus vs
ribosome)
• More chromosomes
• More genes
(20,000-50,000)
No Operons
• Related Genes Separate
Hemoglobin
Beta
chain
Alpha
chain
Beta
chain
Alpha
chain
Beta Gene
Chromosome 11
Alpha Gene
Chromosome 16
Have Introns and Exons
Alpha Hemoglobin Gene
E-I
E-II
Introns
E-III
DNA Packing
• DNA Wraps Around Proteins
• Folds several times
Nucleosome
DNA wrapped 2x around 8 histones
Spacer
Histones
(+ Charge)
DNA - 2 nm
Nucleosome - 11 nm
Solenoid
Ring of nucleosomes
30 nm
Chromatin and Chromosome
Chromosome (Division)
Highly Folded 700 nm
Solenoid
30 nm
Chromatin (Interphase)
Looped Solenoids 300 nm
Chromosome Territories
Each chromosome has own region in nucleus
Heterochromatin vs Euchromatin
• dark-staining
• tightly coiled DNA
• genetically
inactive
•
•
•
•
Found
centromere
telomeres
entire Y
Inactive X (Barr body)
• light staining
• relatively uncoiled
• genetically active
DNA Methylation
addition of -CH3 to base or sugar
Cytosine
Cytosine
NH2
NH2
CH3
O
O
DNA closed, inactive
Chromatin Remodeling
• alteration of DNA association with histones
• necessary for gene transcription
Acetylation
addition of acetyl group to histone
NH3
+
CH2
histone acetyltransferase
HAT
CH2
CH2
Lysine
+ charge
CH2
CH2
NH -CH2-CH3
CH2
histone deacetylase
HDAC
CH2
CH2
Lysine
no charge
less attraction to DNA
Epigenetics
•
Changes in phenotype or gene expression that
do not involve changes in DNA sequences
•
Caused by differences in methylation and
acetylation
Gene Organization
DN
E
P
Gene
S
Promoter - DNA region - RNA polymerase attaches
- upstream
Enhancer - DNA region - increase transcription upstream or downstream or intron
Silencer - DNA region - decrease transcription upstream or downstream or intron
Transcription Factors
• proteins that bind to DNA to affect transcription
IIB
TAFs
TBP
IIA
IIJ
IIF
IIH
IIE
Basal (General)Transcription Factors
Attach to promoter
Attract RNA Polymerase
RNA
IIB
IIF
Polymerase
TBP IIA
TAFs
IIJ
IIH
Promoter
IIE
Activators
• increase transcription
• Some bind to enhancer/promoter to form loop
Enhancer
IIB
TAFs
TBP
IIA
RNA
Polymerase
IIJ
IIF
IIE
IIH
Promoter
Transcription
Video
Activators
• others attract enzymes to open chromatin
HAT
RNA
Polymerase
Repressors
• inhibit transcription
• binds to silencer
• attract enzymes to close chromatin
HDA
R
Transcription Factor Attachment
• environmental signal
• binding of another transcription factor
Phytochrome
•Causes plant responses to light
Pr
TA
Fs
II
J
II frII
IIE
P
Pfr
red light
Estrogen
• female sex hormone
Estrogen
Inactive
Receptor
TA
FsActive II
II J
Receptor
II
IIE
Active
Receptor
Post-Transcriptional Control
1. Alternative Splicing of Exons
mG E1 E2 E3 E5 E6
AAAAAA...
neuropeptide
Brain
E1
mRNA
1o Transcript
E2
E3
E4
E5
thyroid
mRNA
Processed mG E1 E2 E3 E4
Transcript
AAAAAA...
calcitonin
E6
Post-Transcriptional Control
2. RNA Interference (RNAi)
• Process that uses small RNA molecules to
regulate gene expression
• 2 sources of RNA
‣ cell’s own genes - MicroRNA (miRNA)
‣ viruses and transposons - Small Interfering
RNA (siRNA)
MicroRNA
Typical Gene
mRN
Microgene
MicroRNA
DNA
Protein
binds to
Blocks
Transcription
MicroRNA
Dicer
RISC
RNA Interference
http://www.youtube.com/watch?v=_-9pROnSD-A
RNA Interference
siRNA or miRNA
RNA Induced
Silencing Complex
RISC
Complex binds
to mRNA and
stops translation
RNA Induced
Transcriptional Silencing
RITS
complex
Complex binds to
DNA histones and
blocks transcription
Post-Transcriptional Control
2. RNA Interference (RNAi)
• Process that uses small (20-25 bases) RNA
molecules to regulate gene expression
• 2 sources of RNA
‣ cell’s own genes - MicroRNA (miRNA)
‣ viruses and transposons - Small Interfering
RNA (siRNA)
• Process likely evolved to inactivate viral genes
and transposons
Microgene Discovery
scientists trying to genetically engineer
petunia to be darker
got white patches due to RNA interference
MicroRNA Research
C. elegans (roundworm)
grows fast (3 days)
reproduces (3 days)
hundreds of offspring
•Microgenes found in all eukaryotic organisms
•Over 1000 in human genome
•analogous process in bacteria
Potential Uses iRNA
• research into gene function
• pharmaceutical use
• block expression of abnormal gene
• block overexpression of normal gene
(viruses, cancer)
Activity 18
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